The present invention relates to water-in-oil emulsions of a water-soluble polymer, particularly to water-in-oil polymeric emulsions containing an N,N-dialkyl amide of an aliphatic compound.
Various water-soluble polymers such as copolymers of acrylamide and acrylic or methacrylic acid are useful in a variety of applications such as enhanced or secondary oil recovery of petroleum, flocculation of finely divided solids from aqueous suspensions such as sewage, plating waste and potable water, and the like. These water-soluble polymers are often advantageously prepared as water-in-oil emulsions, i.e., a dispersion of polymer containing water droplets in a continuous oil phase. In use, the water-in-oil polymeric emulsion is inverted, such as by the addition of the emulsion to water, to allow the polymer to dissolve in the now continuous water phase and impart a coincident viscosity increase.
Heretofore, to facilitate the inversion of the water-in-oil emulsion and/or dissolution of the water-soluble polymer, it has been proposed to increase the overall HLB of the water-in-oil emulsions. Specifically, although the polymer emulsions are prepared using a surfactant (e.g., an emulsifier which is commonly soluble in the continuous oil phase) such emulsifiers are often not of a sufficiently high HLB value to effectively cause the inversion of the polymeric emulsion in water, particularly in the sea or salt water normally encountered in secondary oil recovery operations.
One method which has been proposed to increase the overall HLB of the emulsion involves reducing the amount of the low HLB emulsifiers employed in the preparation of the water-in-oil emulsion. Alternatively, it has been proposed to employ, as the emulsifier used in the preparation of the water-in-oil emulsion, a surfactant having as high as possible HLB value. Unfortunately, these methods have met with limited success since the amounts and/or HLB value of the emulsifiers employed in the preparation of the emulsion are limited by the requirement that a water-in-oil emulsion must initially be prepared.
Alternatively, to facilitate the inversion of the water-in-oil emulsions and/or the dissolution of the polymer in water, a surfactant having a higher HLB value, a so-called inverting surfactant, has often heretofore been added to the previously prepared emulsion to increase the overall HLB value of the emulsion. This so-called inverting surfactant is particularly necessary to effectively invert the emulsion in the sea or salt waters normally encountered in secondary oil recovery operations.
Unfortunately, the formulated water-in-oil emulsions having the required HLB value for effective inversion in sea or salt water are often not sufficiently fluid to readily flow at low temperatures and/or severe problems are often experienced if the formulations are subjected to repeated freeze-thaw cycling.
In view of these deficiencies in the prior art, it would be highly desirable to provide a water-in-oil emulsion having the required ability to invert in sea water or other aqueous solution having high concentrations of salt, which emulsions exhibit a desired fluidity at low temperatures or when subjected to repeated freeze-thaw cycles.